From: "Malcolm Watts"
Date: Thu, 5 Oct 2000 09:35:44 +1300
Subject: Re: [TSSP] Progress report 28th Sep 2000
On 4 Oct 00, at 14:31, Paul wrote:
MW> > I wonder why the big discrepancy in the measured and
> > predicted value of the spaced coil?
>
> Easy enough when the measured Q is lower than predicted, we
> just propose some additional sources of loss. But what do we do
> with a coil that has a significantly higher Q than allowed by the
> series resistance calculated from Medhurst? Perhaps Mark has
> some comments. I'm stumped.
Agree with comments. The obvious possibility is msmt error. If
the result is consistent across a range of coils and disagrees
with other theoretical approaches, then that calls the
efficacy of all msmts into question.
I have just re-read your piece and see that coil h/d's
are identical and the msmt concerned pertains to the
spacewound coil. That msmt is not outstanding from the rest
for that particular coil. In comparing the two from a point of
pure reason, the decrease in wire diameter is offset by a
reduction in proximity effect and it does not intuitively seem
unreasonable that the two coils are in the same ballpark Q-
wise. Therefore, I would be interested to know what an
approach other than Medhurst suggests and how Medhurst arrives
at his result.
I should point out that the h/d=1 spaced coil agrees
well (in terms of its general characteristics) with what is
known about such a coil, in particular, it does score the
highest Q of the lot with no topload. I am therefore loathe to
condemn that bunch of msmts outright. Luckily, I will have the
opportunity to remeasure a coil very similar to the h/d=4
spaced coil as I have one sitting in my garage (same former
material and diameter - h/d might be a bit less and wire might
be a little larger but spacing is in the ballpark). I will
make a point of checking that one later this year.
> > Towards the end of the year I may just get the opportunity to
> > do some further secondary measurements for you.
>
> Well its going to take some time to absorb the results which you
> and Mark have already sent. A sample of three of these results has
> been enough to break the model nicely! I'm rewriting the laplace
> solver in the hope that it can be made to deal with these better.
> After that I hope to do some studying to try and get underneath the
> Medhurst empirical work.
>
> > I am also planning some measurements to try and resolve
> > issues pertaining to primary "Q" (gap included) with a bunch
> > of series gaps and gap spacings to get a better handle on
> > absolute losses.
>
> Thats some challenge you're taking on there! So many variables.
> Got one of those fancy digital scopes, the ones where you can read
> the trace through an RS232 cable? There must be a lot of information
> hidden in the ringdown envelope.
There is, and yes, I am extremely lucky to have had use of a
good digital scope for quite a few years now. My initial
findings on capturing primary ringdowns several years ago left
me stunned! Gary Lau has now got onto it as well (I am no
longer on the coil builder's list). I realized that as long as
the readings could be taken in a consistent manner, there is
no need for absolute amplitude msmts. The *relative* times and
levels give all the information needed to calculate
differences in proportional losses on a per-cycle basis.
General rules can be derived such as constant (or nearly so)
voltage drop per gap etc. The msmts will be comprehensive but
no more complex than the secondary series I feel.
> > For you this is a side-issue I expect.
>
> Well I try to stay focused on secondary issues, and I know nothing
> about spark gaps, but I'd like to hear more about your plans.
It's more for my interest than anything else. If others want
to know the results, that's fine.
I think the major thing to come out of my secondary
research was that for non-output discharge applications,
secondary characteristics really matter but if one is
designing for long sparks, those considerations, while
important to a certain extent are relegated to the stalls,
because the emphasis now shifts to dealing with the
characteristics of ionized air and how best to make it do what
is required.
Regards,
Malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.